The good news is this means a higher chance of finally getting the 5E books on DMs Guild/DriveThruRPG. (They're so compatible, though, that I could see them not doing it.)
Maybe. Too early to tell I think.
Normally, I believe (from what I understand at least, I may be mistaken) they TRY (in otherwords, there may have been mistakes made) to publish to most recent version of the rules, and hopefully with the included errata if it was officially released in a publication.
This is why 2e has the Newer versions released from the 2010s rather than those from the late 80s and early 90s.
I think in regards to half edition changes, they don't have 3e core available for release (yet at least), but they do have the 3.5 versions available (and PoD as well if you desire).
I think it will depend on what angle they want to take with the 5e and One D&D release. I would assume that right now they are not planning on releasing the current Core books on DMsGuild (I could be wrong, have been before), but obviously, depending on what happens, that could change in the future.
If it is FULLY compatible though, and is basically seen as more of a jump rather than a new edition (being compatible and all) I would expect, in how they've done prior rules, they would not release the books.
On the otherhand, if you go very far back, they HAVE released BX, BECMI, and the RC in PDF format at the same time...though technically you could also say they are different versions/editions of that game as well. Maybe...